diff --git a/Makefile.in b/Makefile.in
index 92b2525d58..66fe98ef33 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -1526,10 +1526,16 @@ fiddle_generated = $(fiddle_html) \
 clean-fiddle:
 	rm -f $(fiddle_generated)
 clean: clean-fiddle
-emcc_flags = -sEXPORTED_RUNTIME_METHODS=ccall,cwrap \
+emcc_opt = -O0
+#emcc_opt = -O1
+#emcc_opt = -O2
+#emcc_opt = -O3
+#emcc_opt = -Oz
+emcc_flags = $(emcc_opt) \
+             -sEXPORTED_RUNTIME_METHODS=ccall,cwrap \
              -sEXPORTED_FUNCTIONS=_fiddle_exec \
+             -sEXIT_RUNTIME=1 \
              --shell-file $(fiddle_tmpl)
 $(fiddle_html): Makefile sqlite3.c shell.c $(fiddle_tmpl)
 	emcc -o $@ $(emcc_flags) sqlite3.c shell.c
-
 fiddle: $(fiddle_html)
diff --git a/ext/fiddle/fiddle.in.html b/ext/fiddle/fiddle.in.html
index a86f07ef76..4568c4b2cf 100644
--- a/ext/fiddle/fiddle.in.html
+++ b/ext/fiddle/fiddle.in.html
@@ -56,6 +56,10 @@
       label {
           cursor: pointer;
       }
+      .error {
+          color: red;
+          background-color: yellow;
+      }
     </style>
   </head>
   <body>
@@ -81,6 +85,7 @@ select * from t;</textarea>
       <div class='ta-wrapper'>
         <textarea id="output" readonly rows="18" placeholder="Shell output"></textarea>
         <div class='button-bar'>
+          <button data-cmd='.help' disabled>Help</button>
           <button id='btn-clear-output' disabled>Clear</button>
         </div>
       </div>
@@ -92,7 +97,6 @@ select * from t;</textarea>
         <label for='opt-cb-sbs'>Side-by-side</label>
       </div>
     </fieldset>
-    <hr>
     <script type='text/javascript'>
       (function(){
           /**
@@ -130,23 +134,30 @@ select * from t;</textarea>
                       doExec(sql);
                   }
               },false);
-              doExec()/*sets up the db and outputs the header*/;
+              doExec(null)/*sets up the db and outputs the header*/;
 
               let e = document.querySelector('#opt-cb-sbs');
               const mainWrapper = document.querySelector('#main-wrapper');
               e.addEventListener('change', function(){
                   mainWrapper.classList[this.checked ? 'add' : 'remove']('side-by-side');
               }, false);
+
+              /* For all buttons with data-cmd=X, map a click handler which
+                 calls doExec(X). */
+              const cmdClick = function(){doExec(this.dataset.cmd);};
+              document.querySelectorAll('button[data-cmd]').forEach(
+                  e => e.addEventListener('click', cmdClick, false)
+              );
           };
 
           /**
-             What follow is part of the emscripten core setup. Do not modify without
-             understanding what it's doing...
+             What follows is part of the emscripten core setup. Do not
+             modify without understanding what it's doing...
           */
-          var statusElement = document.getElementById('status');
-          var progressElement = document.getElementById('progress');
-          var spinnerElement = document.getElementById('spinner');
-          window.Module = {
+          const statusElement = document.getElementById('status');
+          const progressElement = document.getElementById('progress');
+          const spinnerElement = document.getElementById('spinner');
+          const Module = window.Module = {
               preRun: [],
               postRun: [],
               onRuntimeInitialized: function(){
@@ -158,7 +169,7 @@ select * from t;</textarea>
                   }
                   f._.value = ''; // clear browser cache
                   return function(text) {
-                      if (arguments.length > 1) text = Array.prototype.slice.call(arguments).join(' ');
+                      if(arguments.length > 1) text = Array.prototype.slice.call(arguments).join(' ');
                       // These replacements are necessary if you render to raw HTML
                       //text = text.replace(/&/g, "&amp;");
                       //text = text.replace(/</g, "&lt;");
@@ -170,15 +181,15 @@ select * from t;</textarea>
                       f._.scrollTop = f._.scrollHeight; // focus on bottom
                   };
               })(),
-              setStatus: function(text) {
-                  if (!Module.setStatus.last) Module.setStatus.last = { time: Date.now(), text: '' };
-                  if (text === Module.setStatus.last.text) return;
-                  var m = text.match(/([^(]+)\((\d+(\.\d+)?)\/(\d+)\)/);
-                  var now = Date.now();
-                  if (m && now - Module.setStatus.last.time < 30) return; // if this is a progress update, skip it if too soon
-                  Module.setStatus.last.time = now;
-                  Module.setStatus.last.text = text;
-                  if (m) {
+              setStatus: function f(text) {
+                  if(!f.last) f.last = { time: Date.now(), text: '' };
+                  if(text === f.last.text) return;
+                  const m = text.match(/([^(]+)\((\d+(\.\d+)?)\/(\d+)\)/);
+                  const now = Date.now();
+                  if(m && now - f.last.time < 30) return; // if this is a progress update, skip it if too soon
+                  f.last.time = now;
+                  f.last.text = text;
+                  if(m) {
                       text = m[1];
                       progressElement.value = parseInt(m[2])*100;
                       progressElement.max = parseInt(m[4])*100;
@@ -188,23 +199,33 @@ select * from t;</textarea>
                       progressElement.value = null;
                       progressElement.max = null;
                       progressElement.hidden = true;
-                      if (!text) spinnerElement.hidden = true;
+                      if(!text) spinnerElement.hidden = true;
                   }
                   statusElement.innerHTML = text;
               },
               totalDependencies: 0,
               monitorRunDependencies: function(left) {
                   this.totalDependencies = Math.max(this.totalDependencies, left);
-                  Module.setStatus(left ? 'Preparing... (' + (this.totalDependencies-left) + '/' + this.totalDependencies + ')' : 'All downloads complete.');
+                  this.setStatus(left
+                                 ? ('Preparing... (' + (this.totalDependencies-left)
+                                         + '/' + this.totalDependencies + ')')
+                                 : 'All downloads complete.');
               }
           };
-          Module.printErr = Module.print/*redirect stderr*/;
+          Module.printErr = Module.print/*capture stderr output*/;
           Module.setStatus('Downloading...');
-          window.onerror = function() {
+          window.onerror = function(/*message, source, lineno, colno, error*/) {
+              const err = arguments[4];
+              if(err && 'ExitStatus'==err.name){
+                  Module.printErr("FATAL ERROR:", err.message);
+                  Module.printErr("Restarting the app requires reloading the page.");
+                  const taOutput = document.querySelector('#output');
+                  if(taOutput) taOutput.classList.add('error');
+              }
               Module.setStatus('Exception thrown, see JavaScript console');
               spinnerElement.style.display = 'none';
               Module.setStatus = function(text) {
-                  if (text) console.error('[post-exception status] ' + text);
+                  if(text) console.error('[post-exception status] ' + text);
               };
           };
       })();
diff --git a/manifest b/manifest
index 0018bf2e36..570065c9dc 100644
--- a/manifest
+++ b/manifest
@@ -1,9 +1,9 @@
-C Code\sstyle\sfixes:\ss/char\sconst/const\schar/.
-D 2022-05-18T18:10:17.699
+C Improved\shandling/reporting\sof\sconditions\swhich\strigger\san\sexit()\sfrom\snative\scode,\se.g.\scalling\sthe\s'.read'\scommand.\sAdded\sa\sHelp\sbutton\swhich\ssimply\ssubmits\sthe\s'.help'\scommand.\sAdded\scommented-out\svariants\sof\svarious\s-Ox\sflags\sto\ssimplify\sexperimenting\swith\sthem.
+D 2022-05-18T21:18:21.599
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
-F Makefile.in ff32504cde350caaf4d52abfdca5dd1fa88b21e53071a0f9cc3539b6789c3606
+F Makefile.in 92890acbab78c76f32ebb1ad50b961c3fc413f7b05052663c8b17d1b7f74a697
 F Makefile.linux-gcc f609543700659711fbd230eced1f01353117621dccae7b9fb70daa64236c5241
 F Makefile.msc b28a8a7a977e7312f6859f560348e1eb110c21bd6cf9fab0d16537c0a514eef3
 F README.md 8b8df9ca852aeac4864eb1e400002633ee6db84065bd01b78c33817f97d31f5e
@@ -56,7 +56,7 @@ F ext/expert/sqlite3expert.c 6ca30d73b9ed75bd56d6e0d7f2c962d2affaa72c505458619d0
 F ext/expert/sqlite3expert.h ca81efc2679a92373a13a3e76a6138d0310e32be53d6c3bfaedabd158ea8969b
 F ext/expert/test_expert.c d56c194b769bdc90cf829a14c9ecbc1edca9c850b837a4d0b13be14095c32a72
 F ext/fiddle/Makefile ea647919e6ac4b50edde1490f60ee87e8ccd75141e4aa650718c6f28eb323bbc
-F ext/fiddle/fiddle.in.html aef414dcdede5842ae8328bd17aa0d97ee5f592098c1936ce26f9d4d26ab40fa
+F ext/fiddle/fiddle.in.html be6f4402b5b3e6287004b1b4d76c049d1fc0a5ae3b642578241e77e853fda30e
 F ext/fiddle/index.md 08d25ec6fe2a56923e8ea6e5d6c80907bf3a60f9c40a6841a8f402e402dd5f22
 F ext/fts1/README.txt 20ac73b006a70bcfd80069bdaf59214b6cf1db5e
 F ext/fts1/ft_hash.c 3927bd880e65329bdc6f506555b228b28924921b
@@ -1957,8 +1957,8 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P 4eec05457fabe8248b8fd48d6187e772b69429ed64e99f02d0ad6b1230b5835e
-R 827e31b4bc83d11855fefe2a58e8b6d3
+P 9bf042b2eb2137239a59e421e89eb463e719b264eac3db2adae44e321b9a4ad3
+R 7e80413f51d07b2a693b13b3778bbe1a
 U stephan
-Z d569a8b85b6a19a19ff04cd6f21c4eda
+Z 307b97d13682722e9b5c5bfc0074797a
 # Remove this line to create a well-formed Fossil manifest.
diff --git a/manifest.uuid b/manifest.uuid
index 3b661c373b..da2117dbd3 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-9bf042b2eb2137239a59e421e89eb463e719b264eac3db2adae44e321b9a4ad3
\ No newline at end of file
+bf06ddf4125d2726019fa16d312726c8551094be991509499b5688f6a68a7747
\ No newline at end of file
